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1.
A hierarchical series of tidal periodicities are preserved within laminated tidal flat deposits at the barrier/back-barrier
interface of Romney Marsh and the Dungeness Foreland in southeast England. The sedimentary record of the tidal signature,
extracted from variations in sand layer thickness, was found to be severely truncated with neap-spring periods typically represented
by five or less sand layers and possibly only alternate neap-spring periods present. Despite the low number of sand layers
deposited in these higher frequency tidal cycles, semi-annual periods are clearly preserved but tend to contain less than
the expected 6 months of sedimentation. Annual accumulation rates of around 0.2–0.3 m/year are indicated. Local emplacement
of storm beaches is considered to have created the protected conditions suitable for tidal rhythmite preservation. Ongoing
foreland progradation and infilling eventually restricted tidal inundation to the point where distinct sand laminae were no
longer deposited. Here, in contrast with other systems, accommodation space was not limiting and tidal flat elevation is reflected
as a more subtle control on spatial changes in the resolution of the tidal signal. 相似文献
2.
潮水盆地侏罗系沉积特征及找煤潜力 总被引：3，自引：0，他引：3
潮水盆地侏罗系为完整的断陷湖泊充填沉积序列,沉积环境属多种沉积体系,具有低位体系域—湖侵体系域—高位体系域的多层序旋回的特点。下侏罗统为断陷初始形成期的湖泊沉积,具有断陷盆地形成初期“填平补齐”的沉积特点。地层厚度变化大,沉积相变快。在层序中可识别出低位体系域与湖侵早期体系域。低位体系域主要发育了冲积扇、辫状河道、滨浅湖砂砾、洪积物等;中侏罗统为裂陷发展期湖泊沉积,为盆地内主要含煤岩组。层序中粒度旋回较发育,通常在每一旋回的上部含煤层或炭质泥岩,层序底部常发育砾岩。在该层序中可识别出局部低位体系域与高位体系域。低位体系域发育河流砂砾沉积和滨浅湖砂砾,常表现出垂向加积或退积序列。而湖侵体系域则以较深水的湖相沉积为特征,常表现出向上泥岩厚度加大的退积式准层序组;同时,亦发育诸多三角洲相沉积;上侏罗统为断陷消亡期沉积,形成低位体系域浅湖、扇三角洲和冲积扇沉积体系。潮水盆地下侏罗统芨芨沟群上岩组和中侏罗统青土井群下岩组均具有成煤的构造、成煤的环境和成煤的物质来源,而找煤的关键是寻找目前技术、经济水平可以达到的赋煤构造。 相似文献
3.
辽西北票地区义县组古气候环境标志及其意义 总被引：10，自引：2，他引：10
野外地质调查及综合研究表明，包含中华龙鸟、被子植物等珍稀化石的热河生物群的主要赋存层位为义县组二段湖相沉积岩层。对产于不同地点沉积层中的植物、孢粉化石以及木化石进行了总结研究，分析了它们所反映的古气候环境，认为义县组沉积时期存在大量的喜温湿植物，总体指示温暖湿润的生存环境。同时，一些旱生的买麻藤类植物的普遍存在、本内苏铁类的膜质叶以及松柏类的鳞状叶等的特征反映了存在季节性干旱、半干旱气候的可能性。这种气候状况的出现可能与火山活动有关。 相似文献
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A. G. PLINT 《Sedimentology》1984,31(2):213-225
The Lower Headon and Upper Barton Beds of Hampshire, southern England, consist of fine sands, silts and clays, often fossiliferous, with lignitic and carbonate horizons. They accumulated in a coastal environment following deposition of the marine Lower and Middle Barton Beds. A variety of distinctive facies can be defined on faunal and lithological grounds, and these permit palaeoenvironments to be defined with some precision. Littoral marine, barrier island shoreface, storm washover and barrier flat, brackish lagoon, distributary channel and floodplain lake environments are recognized. The evidence suggests that a barrier island or spit developed offshore, enclosing a sheltered inshore region of lagoons in which deposition of relatively fine-grained sediments took place. Lagoonal sediments show a general trend towards reduction of salinity with time. With the eventual exclusion of marine influence, the area underwent a gradual transition to river-dominated sedimentation in shallow flood-plain lakes. While the sequence as a whole shows a progressive reduction in salinity, several brief periods of increased salinity are recognized and these reflect the very low topography of the region and its susceptibility to marine incursion. 相似文献
6.
Yi Yang Bao-sheng Li Shi-fan Qiu Zheng Wu Quan-zhou Gao Yun-zhuo Li 《Geochemistry International》2008,46(1):96-103
This paper analyzes the contents of 16 trace elements in the strata of the Chagelebulu Stratigraphic Section, Badain Jaran Desert, since 150 kyr B.P. and discovered that both the contents of the relatively stable elements, such as P, Mn, Zr, Cr, Pb, Rb, Nb, Y, and the relatively active elements, such as V, Sr, Ni, Cu, Zn, As fluctuated with the sedimentary cycles composed of 25 aeolian dune sands, loess, paleosols, lacustrine facies, alluvial, and colluvial sandy gravels, showing 25 cycles of low-high variation and a fluctuant jagged graph of chemical elements’ migration and accumulation. The lower contents of the elements in the aeolian sands show the erosion, migration and deposition of wind power in a cold and arid climate. The relative accumulation of sandy-gravel layers, especially the lacustrine facies, loess, and paleosols correlates with the section’s position in the special depression relief with a background of warm and humid climate. The above-mentioned variational characteristics were mainly caused by 25 cycles of arid-cold, windy, and warm-humid climatic fluctuation on the southern fringe of the Badain Jaran Desert since 150 kyr B.P. The essential reason bears a relationship with the back and force swing of the East Asia winter monsoon and summer monsoon influenced by climatic vicissitudes during the glacial and interglacial periods. 相似文献
7.
Wave-generated structures and sequences from a shallow marine succession, Lower Carboniferous, County Cork, Ireland 总被引：2，自引：0，他引：2
In a Lower Carboniferous formation south of Cork, Ireland, characterized by sand/mud alternations at varying scales, several lithotypes could be singled out on the basis of relative sand content and primary sedimentary structures. The lithotypes are arranged in several types of sequences: coarsening upwards, coarsening-fining upwards, random, and in rare instances: fining upwards. With increased gross sandcontent the sand intercalations thicken and show a richer array of structures, reflecting a wider range of energy conditions. The majority of the structures is interpreted as wave generated. Current formed structures play an insignificant role. Tidal effects could not be ascertained. The alternation of low- and high-energy lithotypes, occurring in sandy as well as muddy parts of the sequences is explained as resulting from the interplay of storm and fair weather conditions. The effect of shoaling bathymetry is reflected in sequences by an increasing importance of high-energy lithotypes. The environment of deposition can be visualized as a muddy shallow marine platform on which longshore directed sandy shoals were formed under the influence of wave action. Depending on the degree of wave agitation and the availability of sand the shoals reached different stages of maturity: incipient, submerged or emergent. The sequential type encountered in vertical sections depends on the location of the line of logging and varies laterally as sandlenses thicken, amalgamate or die out. 相似文献
8.
Diwakar Mishra 《Journal of Asian Earth Sciences》2009,34(3):310-316
The whole sedimentary succession (ca 600 m thick) of Wagad area ranging in age from Callovian to Early Kimmeridgian has been divided in to three Formations namely Washtawa, Kanthkot and Gamdau in ascending order. Prograding Kanthkot Formation was frequently interrupted by transgressions. Field and petrographic investigations revealed that the Kanthkot Formation represents three fossiliferous marker beds corresponding to Transgressive sequence I; Transgressive sequence II and Transgressive sequence III. These transgressive sequences are composed of two lithounits: medium to coarse grained/gritty, graded to massive, sheetlike, fossiliferous calcareous sandstone (storm lag unit I) and fossiliferous mudrocks (swell lag unit II). The thickness of the unit I varies from 5 to 75 cm and contains mostly convexly oriented shell fragments and whole shell of Pelecypods, Cephalopods and Brachiopods. Unit II (5–15 cm) is distinguished by sheetlike, massive or laminated, yellowish colour, soft fossiliferous mudrocks. This unit is intercalated with moderately bioturbated sandy siltstone. Unit I is dominant over Unit II in the sequences.Study suggests that the transgressive units were deposited close to wave base by high energy storm flows followed by low energy marine swells during transgression. The intense storms played a major role in the distribution of siliciclastics and nonclastic materials. Storms are evidenced by the occurrence of two distinctly different types of units (storm lags and swell lags). High energy levels are characterized by sand dominated sequence, abundance of reworked sediment particles, high proportion broken shells with convex up orientation and erosional and sharp nature of basal contacts of units together with well preserved bioclasts. Sudden short term changes from high to low energy during transgression are explained by the occurrence of medium to coarse grained siliciclastics interbedded with moderately bioturbated mudrocks. Moderately bedded individual strata, high content of coarse clastics along with polished granule size quartz and abundance of comminuted shells indicate a significant change in depositional setting, possibly closure approach of the source of terrigenous fraction or source uplift. Synrift sedimentation in the present study is documented by an abundance of coarse clastics and an over all aggradational nature of transgressive sequences. 相似文献
9.
四川盆地侏罗纪大安寨段沉积时期水体富营养化,形成了介壳灰岩—泥页岩的湖相混积层系,为混积岩沉积机制研究提供了“天然实验室”。综合利用岩心、测井、录井等资料,以川北仪陇—营山地区为研究区,对大安寨段的岩性分类与沉积相展布特征进行研究,并讨论了该湖相混积层系的沉积过程与控制因素。结果表明: 大安寨段湖相混积层系以介壳组分与细粒硅质碎屑(包含黏土矿物)的混杂与交替为主,整体上可划分为一个完整的湖侵—湖退沉积旋回,大一亚段与大三亚段沉积时期介壳滩分布面积较大,大二亚段则广泛发育半深湖—深湖亚相,此外浅水介壳灰岩可在重力流驱动下于深水环境中发生搬运与再沉积作用; 混积过程主要为相混合与间断混合模式,混积作用受控于湖平面升降变化、物质来源、地质营力等因素,湖平面的升降变化控制着不同沉积微相的分布,地震、风暴浪等触发机制引起的重力流沉积促使不同微相与物质来源的沉积物(陆源碎屑搬运、生物—化学碳酸盐沉积、远源细粒物质悬浮等)相互混合,增加了混积岩内部的杂乱程度并扩大了混积岩的平面分布范围。本次研究建立了仪陇—营山地区大安寨段湖相混积层系沉积过程模式,可为陆相页岩油气勘探和相似地质背景下混积作用的成因研究提供借鉴和参考。 相似文献
10.
Distinct stratification patterns in Lower Liassic mudstones are due to the regular occurrence of shell beds, silty/sandy layers and concretionary horizons. The mudstones formed in four depositional environments: (1) a storm dominated shallow marine system; (2) a hemipelagic system; (3) a shallow marine system influenced by climatic changes at astronomical frequencies; and (4) a pro-deltaic offshore transition/shallow marine system. The tectonic setting played an important role in determining the facies sequence, whereas eustatic sea-level changes were of lesser influence. 相似文献
11.
For the Xiamen coast where typhoon frequently occurs, beaches are subject to severe erosion during typhoons. To investigate storm-induced beach profile changes at Xiamen coast, four inner XBeach models were applied using typhoon Dan as a case study. These numerical simulations utilized hydrodynamic and wave conditions determined from larger-scale outer and middle coupled Delft3D-FLOW and SWAN models. The models were validated against historic measurements of tidal level, storm tide, storm surge and beach profiles, thus showing the accuracy of outer and middle models to provide boundary conditions and the reliability of inner models to reflect beach profile changes during a typhoon process. The applicability of this modeling approach to Xiamen coast was verified. The results also demonstrated that an enormous amount of dune face erosion occurred at the selected beaches during the typhoon Dan process and the slopes in the vicinity of zero elevation for the chosen four beach profiles all turned out to be gentler after typhoon Dan. Nevertheless, these beaches suffered different impact degrees and processes during the typhoon influence period. Compared to swash and collision regimes, overwash and inundation regimes have the ability to alter beach profile rapidly in short time. Post-storm beach profile with and without vegetation indicated that vegetation is capable of protecting coastal beaches to some extent. By running the nested models, the simulated results can be employed in the management of the beach system and the design of beach nourishment projects at Xiamen coast.
相似文献12.
Open-coast intertidal deposits and the preservation potential of individual laminae: a case study from east-central China 总被引：3，自引：0，他引：3
Monitoring of sedimentation and erosion was conducted on an open coastal tidal flat on the southern flank of the Yangtze delta. Various elevation references were established in the intertidal zone and monitored intensively for 4 months in order to examine fortnightly and seasonal (calm weather and storm season) sedimentation and erosion. Longer term (100 years) sedimentation and preservation were investigated through examination of cores and trenches. Two different vertical grouping patterns of tidal bedding were distinguished with thinner and thicker sandy laminae. The number of sand-dominated layers and individual muddy and sandy lamina in the cores were compared with theoretically derived sedimentation rates in order to assess long-term preservation potential. Waves, especially high storm waves, have a significant influence on sedimentation and the preservation of intertidal deposits along the open-coast tidal flat. Monitoring during one season indicated that the sand-dominated layer was directly related to storm deposits, while the mud-dominated layer was deposited during calm weather conditions. The variation in sandy lamina thickness was not related to spring–neap tidal cycles during the monitoring period. The assumption of 100% preservation of sandy laminae deposited during every tidal cycle, which has been assumed in previous time-series analyses for the identification of palaeotidal periodicity, was found to be unrealistic along this open-coast tidal flat. Preservation potential decreases as temporal scale increases. During one neap–spring tidal cycle, the preservation potential of individual sandy and muddy laminae was of the order of 10%. Over a period of 100 years, the estimated preservation potential of individual laminae, including both calm weather and storm deposits, decreased to 0·2%. The 100-year preservation potential of storm-induced, sand-dominated layers was estimated to be of the order of 10%. 相似文献
13.
As an important reservoir type in the Bohai Bay Basin, China, lacustrine beach and bar sands which refer to the shallow water complex deposited mainly by nearshore, delta‐rim and buried hill‐related beaches as well as longshore bars were developed in a particular stage in the evolution of those faulted Cenozoic continental depressions. In the Chezhen Depression, for example, the Second Member of the Oligocene Shehejie Formation (abbr. as Es2 hereafter) formed during the rifting‐to‐thermal subsidence transitional stage. Although well developed in Es2, beach and bar sands are difficult to recognize owing to their relative thinness. The paper summarizes sedimentary characteristics of lacustrine beach and bar sands on cores and logs. Low‐angle cross‐stratification, swash stratification, as well as occasional small‐scale hummocky cross‐stratification resulted from storms can be observed in beach and bar sands. The paper distinguishes bars and beaches from each other in Es2 mainly based on the grain‐size, bed thickness, facies succession and log responses. In order to predict the distribution of beach and bars, a chrono‐stratigraphic correlation framework of Es2 in the study strata is established using a high‐resolution sequence stratigraphic approach. Es2 strata are sub‐divided into six medium‐scale cycles and the mapping of the high‐frequency cycles allows the geographic and stratigraphic distribution of both beach and bar sands to be predicted. The study shows that beach and bars are better developed in times of base‐level fall than in base‐level rise. Factors such as lake‐level fluctuation, sediment supply, palaeogeomorphology and palaeowind direction have exerted control on the formation and distribution of beach and bar sands. Finally, the genetic pattern of beach and bar sands in the Es2 unit has been constructed, which provides a foundation for the prediction of beach and bars reservoir in continental basins in general. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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青岛灵山岛下白垩统湖泊风暴沉积与风暴作用 总被引：1，自引：0，他引：1
灵山岛背来石剖面发育了非常典型的湖泊风暴岩和风暴作用。非常典型的丘、洼状构造发育在火山岩底部的砂页岩中。丘状构造呈典型的丘状,规模不一,小者高数厘米,宽数十厘米;大者高2. 4m,宽12. 48m;具有典型的二元结构：底部为灰色或浅灰色的砂砾岩或砂岩;顶部为深灰色 黑色泥岩、页岩或薄层砂岩互层。砂砾岩分选磨圆均很差,砾石主要为片麻岩,直径多在数毫米到3~4cm,呈悬浮式胶结。砾岩底部为凹凸不平的侵蚀面,砾岩向丘状构造两翼变薄甚至尖灭,与下部侵蚀面呈典型的角度交切。丘状构造的上部的细粒层有四个要素：①上凸形态;②丘状交错层理;③下细上粗的二元结构;④底部具侵蚀面。洼状构造也具有典型的洼状,规模也不一,小者高数厘米,宽十余厘米;大者高2. 4m,宽18. 70m,具有下细上粗的（反)二元结构,但底部多为深灰 灰黑色、甚至黑色的泥岩、页岩或夹薄层砂岩,上部多为砂岩、砂砾岩或砾岩。完整的洼状构造也有四个要素：①下凹形态;②或有洼状交错层理;③下细上粗的（反)二元结构;④底部具侵蚀面。丘状构造与洼状构造在空间上相邻共生,但不是同时形成的,一个连续的完整序列是丘状构造形成在先,洼状构造形成在后,其间由一个粒度较细的薄层分隔开（风暴最高水位时的“静”水沉积)。基于实验和丘洼构造参数计算了风暴浪的相关参数。 相似文献
17.
Quaternary sedimentology of the Rose Creek fan delta, Walker Lake, Nevada, USA, and implications to fan-delta facies models 总被引：1，自引：0，他引：1
The 3·2 km long Rose Creek fan delta of west‐central Nevada is prograding from an active rift margin into the 32 m deep Walker Lake. A case study of the forms, processes and facies of this fan delta reveals that the proximal and medial zones mainly are of sub‐aerial origin, and the distal zone is of lacustrine origin. Pebbly to bouldery rock‐avalanche mounds >100 m thick (Facies A) and muddy to bouldery debris flow levées 0·5 to 2·0 m thick (Facies B) dominate the proximal zone, whereas mostly matrix‐supported cobbly pebbly debris flow lobes 0·1 to 1·0 m thick (Facies C) typify the medial zone. Surficial pebble lags and gully fills (Facies D) are widespread in both zones but, in exposures, comprise only partings or lenticles between debris flow units. The distal fan delta mainly consists of lakeshore to lake‐bottom tracts formed by extensive wave reworking of debris flow facies. Nearshore deposits include erosional cobbly boulder lag beaches (Facies E), pebbly constructional beaches attached at headcuts or on barrier spits (Facies F), pebbly upper shoreface (Facies G) and sandy lower shoreface (Facies H) tracts positioned lakeward of the beach, and pebbly landward‐dipping foresets (Facies I) and backshore‐pond sand and mud (Facies J) present landward of the spits. Erosional lag beaches fringe the windward north side of the fan‐delta front, attached constructional beaches characterize the central zone, and southward‐elongating barrier spits typify the leeward south side, extending from the zone of greatest projection of the fan delta into the lake. Shoreline facies asymmetry results from largely unidirectional longshore drift caused by high fetch to the north and minimal fetch to the south, combined with the arcuate shape of the fan‐delta front. The spits overlie a platform deposited below common wave base consisting of south‐east‐trending cones of pebbly Gilbert foresets (Facies K) and sandy toesets (Facies L). Typically slumped silt and mud (Facies M) fringe both this platform and lower shoreface sand in deeper water. This case demonstrates facies types and patterns that are inconsistent with the widely promoted fan‐delta facies model having a front consisting of an apron of radially directed Gilbert foresets deposited where sub‐aerial flows enter the lake. The Rose Creek fan‐delta front instead features a sharp contact between sub‐aerial and lakeshore facies formed where waves erode, sort and redistribute heterogeneous debris flow sediment into the various shallow‐to‐deep lake facies. Gilbert foresets are present only in the lee of the fan delta where sediment moving by longshore drift reaches the brink of the spit front. This facies scenario results from the infrequency of fan‐building events versus nearly constant wind‐induced waves, a scenario that, in contrast to the popular Gilbert model, probably is the norm for fan deltas. The level of Walker Lake, and thus the position of wave reworking on the Rose Creek fan delta, fluctuated over a range of ～157 m during the last 18 kyr, producing complex interfingering between sub‐aerial and lakeshore facies across a 1700 m wide radial belt, typifying a wave‐modified, freestand lacustrine fan delta. 相似文献
18.
本数据集是作者2017年在银川盆地平罗站幅施工的14个工程地质钻孔岩心中采集的234个岩土样品,经过测试分析后所得的共2 602组测试数据。这些数据主要体现了土体的抗剪强度、压缩模量、颗粒成分等。图幅内第四系分布广泛,厚度大,为区内主要的工程地质岩组,且成因多样,从西到东主要包括：上更新统洪积层,岩性主要为砾石、砂砾石;全新统灵武组细砂土;全新统湖沼积层,岩性主要为淤泥、砂质粘土及粉砂;全新统风积层,岩性主要为土黄色中-细砂、粉砂。其中,全新统灵武组占据了图幅大部分区域,岩性主要为细砂、粉砂、砂质粘土等。钻孔揭示,银川平原区地层纵向上以河湖相细砂、粉砂为主,夹粉质粘土,局部钻孔含卵砾石层。样品测试数据分析显示,图幅区内碎石土、冲积砂土、粘性土具较高的抗剪强度,工程地质条件较好;而图幅西北部砂岩、泥岩由于中等到强风化程度,且有软弱夹层,工程地质条件较差。湖沼积成因的淤泥、砂质粘土及粉砂工程地质性质亦较差。本次图幅区内的工程地质钻探工作施工规范,测试分析均由具备国家资质的实验室承担,得到的数据质量可靠,真实反映了该区域内地层信息及岩土物理力学性质。 相似文献
19.
《Quaternary Science Reviews》2007,26(22-24):2913-2923
This paper provides sedimentological details of the Salto depositional sequence of western Uruguay, which includes the Salto and the Bellaco Formations. These units are interpreted as evidence, in the Uruguayan landscape, of a Pleistocene forebear of the Uruguay River. The Salto depositional sequence, encompasses two depositional cycles: (a) the lower cycle, represented only by the Salto Formation, with conglomeratic sandstones and sandstones intercalated with pelites and fine sandstones; and (b) the upper cycle, represented by the Salto Formation and the Bellaco Formation, characterized by conglomerates and conglomeratic sandstones with horizontal stratification, discontinuous silicified sandy levels and gypsum–clay bodies. The Salto sequence is characterized by braided river deposits, genetically associated with lacustrine or palustrine and possible aeolian sediments. Cyclic alternations of channelized tractive currents and interchannel contexts are indicated. A possible Pleistocene age for the Salto Formation is discussed, in the light of new and preliminary information (thermoluminescence ages) from the lower cycle. There are several lines of evidence indicating semi-arid conditions during the ‘Salto event’. Comments on regional correlation are provided, as well as the effects of neotectonic processes. 相似文献
20.
Ricardo Hernandez-Moreira Sadegh Jafarinik Sydney Sanders Christopher G. St. C. Kendall Gary Parker Enrica Viparelli 《Sedimentology》2020,67(4):1951-1972
Turbidity current and coastal storm deposits are commonly characterized by a basal sandy massive (structureless) unit overlying an erosional surface and underlying a parallel or cross-laminated unit. Similar sequences have been recently identified in fluvial settings as well. Notwithstanding field, laboratory and numerical studies, the mechanisms for emplacement of these massive basal units are still under debate. It is well accepted that the sequence considered here can be deposited by waning-energy flows, and that the parallel-laminated units are deposited under transport conditions corresponding to upper plane bed at the dune–antidune transition. Thus, transport conditions that are more intense than those at the dune–antidune transition should deposit massive units. This study presents experimental, open-channel flow results showing that sandy massive units can be the result of gradual deposition from a thick bedload layer of colliding grains called sheet flow layer. When this layer forms with relatively coarse sand, the non-dimensional bed shear stress associated with skin friction, the Shields number, is larger than a threshold value approximately equal to 0·4. For values of the Shields number smaller than 0·4 the sheet flow layer disappeared, sediment was transported by a standard bedload layer one or two grain diameters thick, and the bed configuration was characterized by downstream migrating antidunes and washed out dunes. Parallel laminae were found in deposits emplaced with standard bedload transport demonstrating that the same dilute flow can gradually deposit the basal and the parallel-laminated unit in presence of traction at the depositional boundary. Further, the experiments suggested that two different types of upper plane bed conditions can be defined, one associated with standard bedload transport at the dune–antidune transition, and the other associated with bedload transport in sheet flow mode at the transition between upstream and downstream migrating antidunes. 相似文献